Air filter housing with means for measuring particle concentration

ABSTRACT

An air filter housing ( 1 ) has at least one filter chamber ( 2, 3 ) for receiving at least one filter unit (F), the filter chamber having an inlet end and an outlet end, and elements ( 18, 19 ) for measuring particle concentration in the air leaving the filter chamber. The measuring elements ( 18, 19 ) include a row of several particle detectors ( 20 ) affixed to a common support ( 21 ), members ( 23 - 31 ) for moving the support in a direction perpendicular to the row of detectors, and members for connecting each of the detectors to a counter.

TECHNICAL FIELD

The present invention relates to an air filter housing having at leastone filter chamber for receiving at least one filter unit, said filterchamber having an inlet end and an outlet end, and means for measuringparticle concentration in the air leaving the filter chamber.

BACKGROUND OF THE INVENTION

Filter housings according to the introduction are known from filteringdevices for certain laboratories or the like in which there is a riskthat the ambient air will be contaminated. In order to prevent air fromsuch environment to leak out, such laboratories often are set undersub-pressure. The function of the filter is to capture all infectiousparticles or other contaminations, such as bugs or other air carriedinfectious organisms, in the circulated air. It is thus essential thateach filter functions properly and the integrity of the filters istherefore continuously (periodically?) checked.

It is known to use a particle detector being movable over the outletarea of a filter chamber to check if particles are present in the airleaving the filter in order to detect a leak in the filter media andwhere such a leak is located. A problem with such an arrangement is thatthe mechanism for moving the detector will have a complicatedconstruction and be hard to manoeuvre.

An objective of the present invention is to provide means for measuringparticle concentration in the air leaving the filter chamber in a filterhousing of the kind mentioned above which means are of a simpleconstruction and easy to manoeuvre.

SUMMARY OF THE INVENTION

This objective is accomplished by an air filter housing having at leastone filter chamber for receiving at least one filter unit, said filterchamber having an inlet end and an outlet end, and means for measuringparticle concentration in the air leaving the filter chamber,characterised in that said measuring means includes a row of severalparticle detectors affixed to a common support, means for moving saidsupport in a direction perpendicular to said row of detectors, and meansfor alternately connecting each of said detectors to a counter.

According to a preferred embodiment said moving means are a screw andnut mechanism. Especially, said support is a bar having holes with aninner thread in opposite ends thereof and said means for moving said barare rods with an external thread fitting into said holes in said bar,said rods being rotatably mounted in the filter housing, and drive meansfor synchronously rotating said rods. Said drive means can be anelectric motor coupled to one of said rods and a belt in engagement withdrive wheels on both of said rods. A belt tensioner is advantageouslydisposed in the pass of the belt between the two drive wheels.

In a variant, each rod can be driven by a separate electric motor.

Said detectors are preferably mounted on said support moveable between afirst and a second position in a direction parallel to the flowdirection in the filter unit, whereby the detectors are biased bysprings to the first position.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall now be described with reference to the enclosedFigures, of which;

FIG. 1 schematically discloses a perspective view of an air filterhousing according to a preferred embodiment of the invention with thedoors for the access openings to the two filter chambers being opened,

FIG. 2 schematically discloses a side view partially in section of theair filter housing in FIG. 1,

FIG. 3 a sectional view along line II-III in FIG. 2, and

FIG. 4 schematically discloses a side view partially in section of apart of the air filter housing in FIG. 1.

DESCRIPTION OF EMBODIMENTS

In FIG. 1, a schematic perspective view of an air filter housing 1according to a preferred embodiment of the present invention is shown.In the preferred embodiment, the housing includes two filter chambers2,3 in each of which an air filter unit F is disposed. Access to filterchambers 2,3 is gained by access openings 4,5. These access openings areclosable by doors 6,7 shown in their open position in FIG. 1.

In FIG. 2, the filter housing 1 is shown in a partially sectioned planview seen from the side of the housing 1 containing the access openings4,5. The doors 6,7 are not shown in FIG. 2. As can be seen in FIG. 2,each filter unit F comprises a circumferential wall surrounding thefilter media and ensuring that air passing through the filter unit willnot sidewise leak out of the filter unit but pass through the unit fromone end to the other, i.e. in the longitudinal direction of the filterhousing 1. In FIG. 2 the upper U and lower part L of thiscircumferential wall of a filter unit F disposed within filter chamber 2are shown. When the filter is in operation, the filter units F are heldin the filter chambers 2,3 by clamping devices 8 and 9, respectively.

Clamping device 8 consists of a frame 10 which is movable back and forthin the flow direction of the air or gas passing through the filter unitF. In the preferred embodiment shown, the means for moving the frame 10are four pneumatic cylinders 11, of which two are shown in FIG. 2. Thesepneumatic cylinders can be disposed in the corners of the rectangularframe 10 or in pairs distanced from the corners on the upper and lowerframe parts or the side parts of the frame, as is shown in FIG. 3. It isof course possible, but not preferred, to use more than four pneumaticcylinders and also possible to use three cylinders disposed in atriangular pattern. In FIG. 2 the frame 10 is shown in its operativeposition in which the frame 10 presses the distal end of the filter unitF, i.e. the end being distal from the frame, against a first end wall ofthe filter chamber 2 and is itself pressed against the proximal end ofthe filter unit. The filter unit F is provided with sealing elements(not shown in the Figures), such as sealing rings or the like, affixedto the opposite ends of the circumferential wall surrounding the filtermedia. The frame 10 is biased towards the operative position bycompression springs 12 acting on the piston of each cylinder 11. Thesealing elements on each end of the filter unit F is somewhat compresseddue to the compressive force from the springs 12 thereby ensuring thatair entering the filter housing can not leak out between the first endwall of the filter chamber 2 and the distal end of the circumferentialwall of a filter unit F placed in the filter chamber or between theproximal end of this wall and the frame 10. Each cylinder 12 alsocontains connections (not shown) to a pressure source for moving thepistons of the cylinders 11 against the force of the springs 12 andthereby move the frame 10 to the right in FIG. 2 when a filter unit Fplaced within the filter chamber 2 is to be discharged and replaced by afresh filter unit.

A circumferential flange 14 is projecting inwardly from the outer wallof the filter housing 1 in the second end of the filter chamber 2. Inthe operative position of the frame 10, a portion 15 of the frame 10 isin abutment with the flange 14 via a sealing element. This sealingelement, for example an O-ring, can be affixed to flange 14 or frame 10.By this arrangement it is ensured that air or gas that have passedthrough the filter unit F placed within the filter chamber 2 can notenter the space outside the circumferential wall of the filter unit,i.e. the space to the left of flange 14 or the space between the firstend wall of the filter chamber and the flange 14 in FIG. 2. This spacecontains the access opening 4 to the filter chamber. Thereby it isensured that no contaminated air or decontamination gas will leak out ofthe access opening during operation of the filter or thereafter even ifthe sealing of the access opening is not tight. A double security isthus obtained.

In order to be able to push a filter unit F towards the end wall of thefilter chamber 2, i.e. to the left in FIGS. 1 and 2, the frame 10 has afirst tubular part 17 having an outer circumference smaller than aninner circumference of the circumferential flange 14 and a secondtubular part 15 having an outer circumference larger than the innercircumference of the circumferential flange 14, the second tubular parthaving a smaller longitudinal extension than the first tubular part 17and being disposed in the portion of the frame 10 being proximal to thepneumatic cylinders 11. Thereby, the part 17 can be moved in thelongitudinal direction without being obstructed by the flange 14. Thewidth of the second tubular part 15 is chosen such as the O-ring affixedto the frame or the flange is compressed when the frame 10 is inoperative position pressing the filter unit F against the first end wallof the filter chamber 2.

The second filter chamber 3 is constructed the same way as filterchamber 2 and includes also a clamping device 9 similar to the clampingdevice 10,11 described above.

A device 18,19 for monitoring the integrity of the filter unit F infilter chambers 2 and 3 is mounted in the filter housing 1 at the outletfrom the respective filter chamber 2,3. The monitoring device 19 isidentical to the device 18.

The integrity of the filter unit is monitored by measuring the particleconcentration in the air leaving the filter unit in order to establishif the filter is leaking, i.e. if one or more holes in the filter mediaallow particles to pass through the filter media. It is also importantto locate even very small leaks which means that the particleconcentration in relatively small volumes of air must be studied. Themonitoring device 18 therefore comprises OPC:s (Optical ParticleCounter) sampling relatively small volumes of the air leaving the filterunit F. In order to cover the whole area of the filter unit, the OPC:sneed to be movable so that all air leaving the filter unit will bemonitored by the device 18.

The device 18 comprises a row of several detectors (OPC:S) 20 mounted ona tubular bar 21 with a rectangular cross-section. The inlet end of eachdetector 20 comprises a funnel 22 having circular cross-sections and therow of detectors comprise as many detectors as needed for the funnels tocover the whole length of a side of the outlet area of filter chamber 2.In the disclosed embodiment four detectors are present in the row ofdetectors 20. The numbers of detectors needed is of course dependent onthe length of the side of the area to be covered but also on the size ofthe funnel 22 which means that both more or fewer detectors can be usedwithin the scope of invention. The term “several” means in this context“at least two”.

In order to cover the whole area of the outlet from the filter chamber,the row of detectors is movable from one side of the outlet area of thefilter chamber to the opposite side thereof. To accomplish this, tworotatable rods 23,24 having an external thread over the major part oftheir length are threaded into holes 25,26 in the respective ends of bar21, said holes 25,26 having an inner thread. Thus, by rotating the rods23,24 in one or the other direction, the bar 21 and thereby thedetectors 20 will move towards or away from the side of the outlet areaof the filter chamber, i.e. to the left or right in FIG. 3. The rods23,24 are rotatably mounted in opposite side walls of filter housing anddrivingly in connection with each other via a belt 27 acting on drivewheels 28,29. The end of rod 23 is connected to the output shaft of anelectric motor 30. Rotation of rod 23 by the motor 30 is thussynchronously transmitted from the drive wheel 28 to rod 24 via the belt27 acting on the drive wheel 29.

A belt tensioner 31 is preferably arranged in the path of the belt 27.Said tensioner is schematically shown in FIGS. 3 and 4 and comprises aspring device (not shown) biasing the middle of the three rollersdisclosed in FIG. 4 to the right in FIG. 4 as indicated by andouble-arrow in this Figure. However, any type of belt tensioner can beused.

By appropriate control of the electric motor 30, the row of detectors 20can thus be moved from one side to the other side of the outlet area ofthe filter chamber and back again. During a movement from a first sideto the opposite, second side of the outlet area of the filter chamberonly one of the detectors 20 is connected to a central counter (notshown) which calculates the particle concentration based on the numberof signals from the detector and the flow rate of the air flowingthrough the detector and stores the values calculated this way. When onedetector 20 has traveled from one side to the other side of the outletarea of the filter chamber, the central counter switch from thisdetector to the next detector 20 in the row and registers the values ofthe particle concentration from the latter detector during the returntravel of the row of detectors from the second side to the first side.Thereafter, the next detector in the row is connected to the centralcounter and during the return travel of the row of detectors the last ofthe detectors 20 is connected to the counter.

Since each detector 20 only travels in a straight line, the movingmechanism for the detectors can be of extremely simple construction andbe both accurate and reliable. Reliability is a very important factorfor a filter housing used in a contaminated environment.

As is evident from FIG. 2, the openings of the funnels 22 of thedetectors 20 lie in the same plane as the right edge of the frame 10 andportions of the funnels are also extending over said frame. In FIG. 2,the frame 10 is shown in its operative position clamping the filter unitF but when a used filter unit is to be discharged and substituted by afresh one, the frame 10 is moved to the right in FIG. 2 with the aid ofthe pneumatic cylinders 11. In order to allow such a movement of theframe 10, the detectors 20 are movably attached to bar 21 so that theycan follow the movement of the frame 10 from operative to inoperativeposition. This is for example accomplished by mounting the detectorsslidable within holes in the bar 21. Preferably, the detectors 20 arebiased towards the operative position of frame 10 by springs.

The described embodiment can of course be modified in several wayswithout leaving the scope of invention. For example, the funnels 22 canhave another cross-sectional shape than circular, e.g. rectangular orsquare, and other conicity than shown in FIG. 2. The bar 21 can alsohave another cross-sectional shape than rectangular, for examplecircular or oval, in order to have a more aerodynamic shape. The beltdrive of rod 24 can be deleted and this rod be without an externalthread in which case the hole 26 will be without inner thread. Themovement of the bar 21 will then be performed only by the electric motor30 and the rod 24 will only function as a guide rod. It is of coursealso possible to use one electric motor for each of the rods 23,24.Other types of detectors than OPC:s can be used. Furthermore, thecentral counter can be programmed to simultaneously read the signalsfrom all of the detectors instead of only one detector at a time. Thepresent invention should therefore only be restricted by the content ofthe enclosed patent claims.

1. An air filter housing (1) having at least one filter chamber (2,3)for receiving at least one filter unit (F), said filter chamber havingan inlet end and an outlet end, and means (18,19) for measuring particleconcentration in the air leaving the filter chamber, characterised inthat said measuring means (18,19) include a row of several particledetectors (20) affixed to a common support (21), means (23-31) formoving said support in a direction perpendicular to said row ofdetectors, and means for connecting each of said detectors to a counter.2. An air filter housing (1) according to claim 1, wherein said movingmeans (23-31) are a screw and nut mechanism.
 3. An air filter housing(1) according to claim 2, wherein said support is a bar (21) havingholes (25,26) with an inner thread in opposite ends thereof and saidmeans for moving said bar (21) are rods (23,24) with an external threadfitting into said holes in said bar, said rods being rotatably mountedin the filter housing, and drive means (27-31) for synchronouslyrotating said rods.
 4. An air filter housing (1) according to claim 3,wherein said drive means is an electric motor (30) coupled to one (23)of said rods (23,24) and a belt (27) in engagement with drive wheels(28,29) on both of said rods.
 5. An air filter housing (1) according toclaim 4, wherein a belt tensioner (31) is disposed in the pass of thebelt (27) between the two drive wheels (28,29).
 6. An air filter housing(1) according to claim 3, wherein each rod is driven by a separateelectric motor.
 7. An air filter housing (1) according to claim 1,wherein said detectors (20) are mounted on said support (21) moveablebetween a first and a second position in a direction parallel to theflow direction in the filter unit (F), whereby the detectors (20) arebiased by springs to the first position.
 8. An air filter housing (1)according to claim 2, wherein said detectors (20) are mounted on saidsupport (21) moveable between a first and a second position in adirection parallel to the flow direction in the filter unit (F), wherebythe detectors (20) are biased by springs to the first position.
 9. Anair filter housing (1) according to claim 3, wherein said detectors (20)are mounted on said support (21) moveable between a first and a secondposition in a direction parallel to the flow direction in the filterunit (F), whereby the detectors (20) are biased by springs to the firstposition.
 10. An air filter housing (1) according to claim 4, whereinsaid detectors (20) are mounted on said support (21) moveable between afirst and a second position in a direction parallel to the flowdirection in the filter unit (F), whereby the detectors (20) are biasedby springs to the first position.
 11. An air filter housing (1)according to claim 5, wherein said detectors (20) are mounted on saidsupport (21) moveable between a first and a second position in adirection parallel to the flow direction in the filter unit (F), wherebythe detectors (20) are biased by springs to the first position.
 12. Anair filter housing (1) according to claim 6, wherein said detectors (20)are mounted on said support (21) moveable between a first and a secondposition in a direction parallel to the flow direction in the filterunit (F), whereby the detectors (20) are biased by springs to the firstposition.